Wireless cellular communication networks incorporate a number of mobile UEs and a number of NodeBs. A NodeB is generally a fixed station, and may also be called a base transceiver system (BTS), an access point (AP), a base station (BS), or some other equivalent terminology. As improvements of networks are made, the NodeB functionality evolves, so a NodeB is sometimes also referred to as an evolved NodeB (eNB). In general, NodeB hardware, when deployed, is fixed and stationary, while the UE hardware is portable.
In contrast to NodeB, the mobile UE can comprise portable hardware. User equipment (UE), also commonly referred to as a terminal or a mobile station, may be fixed or mobile device and may be a wireless device, a cellular phone, a personal digital assistant (PDA), a wireless modem card, and so on. Uplink communication (UL) refers to a communication from the mobile UE to the NodeB, whereas downlink (DL) refers to communication from the NodeB to the mobile UE. Each NodeB contains radio frequency transmitter(s) and the receiver(s) used to communicate directly with the mobiles, which move freely around it. Similarly, each mobile UE contains radio frequency transmitter(s) and the receiver(s) used to communicate directly with the NodeB. In cellular networks, the mobiles cannot communicate directly with each other but have to communicate with the NodeB.
Control information feedback bits are transmitted, for example, in the uplink (UL), for several purposes. For instance, Downlink Hybrid Automatic Repeat ReQuest (HARQ) requires at least one bit of ACK/NACK transmitted in the uplink, indicating successful or failed circular redundancy check(s) (CRC). Moreover, a one bit scheduling request indicator (SRI) is transmitted in uplink, when UE has new data arrival for transmission in uplink. Furthermore, an indicator of downlink channel quality (CQI) needs to be transmitted in the uplink to support mobile UE scheduling in the downlink. While CQI may be transmitted based on a periodic or triggered mechanism, the ACK/NACK needs to be transmitted in a timely manner to support the HARQ operation. Note that ACK/NACK is sometimes denoted as ACKNAK or just simply ACK, or any other equivalent term. This uplink control information is typically transmitted using the physical uplink control channel (PUCCH), as defined by the 3GPP working groups (WG), for evolved universal terrestrial radio access (EUTRA). The EUTRA is sometimes also referred to as 3GPP long-term evolution (3GPP LTE). The structure of the PUCCH is designed to provide sufficiently high transmission reliability.
In addition to PUCCH, the EUTRA standard also defines a physical uplink shared channel (PUSCH), intended for transmission of uplink user data. Since PUSCH is designed for transmission of user data, re-transmissions are possible, and PUSCH is expected to be generally scheduled with less stand-alone sub-frame reliability than PUCCH.
Similarly, a physical downlink control channel (PDCCH) and a physical downlink shared channel (PDSCH) are defined for downlink control and data transfers. The modulation schemes supported in the downlink and uplink shared channels are QPSK, 16 QAM and 64 QAM, depending on channel conditions. The general operations of the physical channels are described in the EUTRA specifications, for example: “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (TS36.211, Release 8).”
Error-control coding techniques detect and possibly correct errors that occur when messages are transmitted in PUSCH and PDSCH. To accomplish this, the encoder transmits not only the information symbols but also extra redundant parity symbols. The decoder interprets what it receives, using the redundant symbols to detect and possibly correct whatever errors occurred during transmission.
Block coding is a special case of error-control coding. Block-coding techniques map a fixed number of message symbols to a fixed number of code symbols. A block coder treats each block of data independently and is a memory-less device. The information to be encoded consists of message symbols and the code that is produced consists of codewords. Each block of K message symbols is encoded into a codeword that consists of N message symbols. K is called the message length, N is called the codeword length, and the code is called an [N,K] code.
Turbo codes are a class of high-performance error correction codes developed in 1993 which are finding use in deep space satellite communications and other applications where designers seek to achieve maximal information transfer over a limited-bandwidth communication link in the presence of data-corrupting noise. The channel coding scheme for transport blocks in LTE is Turbo Coding with a coding rate of R=⅓, using two 8-state constituent encoders and a contention-free quadratic permutation polynomial (QPP) turbo code internal interleaver. Trellis termination is used for the turbo coding. Before the turbo coding, transport blocks are segmented into byte aligned segments with a maximum information block size of 6144 bits. Error detection is supported by the use of 24 bit CRC. The ⅓ coding rate triples the bit-count for transmission of the block.